Iraqis arrested by coalition forces have disappeared into a 'black hole' with no records of where they are being held, Tony Blair's personal envoy on human rights has warned.

Ann Clwyd said if the scandal of the missing prisoners had been taken more seriously from the start by the US, it could have helped prevent the abuse of detainees in their jails.

In an interview with The Observer, the Labour MP said she was 'very unhappy' at the rising numbers still detained - and called on the Iraqi government to publish a report on claims that inmates were tortured by Iraqi jailers.

Clwyd, appointed after decades of campaigning against Saddam Hussein's regime, reports directly to the Prime Minister and has until now rarely discussed her work.

She has spoken out amid growing criticism of Britain's failure to stop abuses in Iraq, arguing that suggestions Blair was unwilling to confront the US administration on such issues were wrong: 'I know, in conversations he has with the people of influence in the US, he doesn't pull his punches. He pushes them, sometimes with direct results.'

Clwyd's own files include two alarming cases highlighting the issue of the missing - and the scale of effort required to trace them.

The first involves an elderly woman arrested shortly after the war in the middle of the night by US soldiers. With her family unable to find her, relatives in Britain sought Clwyd's help.

'I spent days and weeks trying to trace where this woman was,' said Clwyd.

'Eventually it meant a visit to Washington, going into the White House and talking to people like [national security adviser] Steve Hadley, [former deputy defence secretary] Paul Wolfowitz and [former US envoy to Iraq] Paul Bremer.' Still, she drew a blank.

Finally Wolfowitz ordered an investigation in Iraq: the woman was traced to a US-run prison near Baghdad airport and freed. She had, according to Clwyd who interviewed her afterwards, been abused in custody: as a Muslim, the shame was such that she would not be identified. 'She was obviously very unsure of herself, emotional, confused: she was frightened. She wanted to put it all behind her.'

The second case involves an elderly man who disappeared in 2004, and was reportedly sighted in a US prison. His son, a British resident, contacted Clwyd. She raised the case in Washington last autumn but so far there has been no trace of him.

Clwyd admitted she did not know how many other similar cases there could be among those arrested on suspicion of being an insurgent or a security threat.

'Mistakes were being made,' she said. 'People were being scooped up - [although] that was all at a time when they were still looking for some of the most wanted.'

The 'tremendous effort' required to trace the missing worries her. 'You did feel that people were disappearing into black holes and it's very difficult.'

Clwyd appears to suspect incompetence, not malice, in the disappearances. Detainees' names were noted by US officials 'sometimes in Arabic, sometimes not, sometimes in bad Arabic', making matching them with the missing difficult.

None the less, she argued, the Americans should have taken the cases more seriously: 'If they had followed it up harder at the time I think it might have avoided some of the allegations - and proof - of abuse that took place.'